Modeling of dissolution kinetics of rare earth crystals in a borosilicate glass melt

The novelty of this work is the comparison of two methods to determine the dissolution kinetics in order to evaluate the applicability of the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model for the crystals dissolution in silicate melts. For this, this work focuses on the dissolution of rare earth (RE) silicates (Ca2RE8(SiO4)6O2 where RE = Nd) with an apatite structure in a sodium-borosilicate glass melt. The first approach consists in the characterization of the dissolution kinetics by following the crystalline area fraction by image analysis as a function of time and temperature. Then, a model based on the generalized JMAK equation is proposed to fit the experimental data. This model enables to determine both the mechanism limiting the dissolution (i.e. the diffusion) and the activation energy of crystals dissolution in the studied glass system (496 kJ/mol). To support these results, a second and most common approach is the measure of the chemical profiles at the crystal/melt interfaces by microprobe. The conclusions obtained by this last method are in agreement with the conclusions based on JMAK model. All these results allowed to confirm that the JMAK model is well suited to model crystals dissolution in silicate melts.